Conventionally, a clutch configured to switch states of power transmission between an outer wheel and an inner wheel, which is arranged on the inner side of the outer wheel, is known (for example, Patent Document 1). In the clutch, an annular holding device, which accommodates rollers each serving as an engagement element, is arranged in the space in which the outer wheel and the inner wheel face each other. Flat cam surfaces are provided on an outer circumferential surface of the inner wheel. The cam surfaces provide wedge-shaped spaces, each of which becomes gradually narrower toward the opposite circumferential sides, between the cam surfaces and the outer wheel.
To couple the inner wheel and the outer wheel to each other, the clutch rotates the holding device together with the outer wheel to pivot the holding device relative to the inner wheel, thus moving each of the rollers, which are accommodated in the holding device, into a narrow space in the corresponding one of the aforementioned wedge-like spaces. The rollers are thus clamped between the inner wheel and the outer wheel such that the inner wheel and the outer wheel are coupled together by the rollers. As a result, the inner wheel and the outer wheel rotate integrally.
In contrast, to decouple the inner wheel and the outer wheel from each other, the holding device and the outer wheel are decoupled from each other. This causes an urging member, which is coupled to the inner wheel, to press and return the holding device to move each roller, which is accommodated in the holding device, from the narrow space into a large space in the corresponding wedge-like space. This causes the rollers to roll between the inner wheel and the outer wheel. As a result, the inner wheel and the outer wheel are disengaged from each other, and power transmission between the inner wheel and the outer wheel is canceled.